Formulating Optimal Size of Cities with Urban Sprawl pattern considering current Trend of Growth (Case study: The Coastal city of Deylam)

After the Industrial Revolution, advancement in industry and technology was coupled with population growth, and rural-urban immigration caused the extreme expansion of cities. Moreover, the rapid growth of urbanization in coastal areas and conflict of interest between the stakeholders has imposed extreme ecological pressure on this fragile ecosystem, which indicates the contrast between cities and coastal environments. According to records from the Statistical Centre of Iran, the coastal city of Deylam, Iran, located in Bushehr Province, has been struggling with population and immigration growth during the past six decades. Since the common expansion pattern of coastal cities is linear, where they are distributed along the coast, any attempt against the urban sprawl of coastal cities will clearly benefit the coastal ecosystem. In this research, the urban sprawl of Deylam was investigated for an approximate time span of ten years using quantitative data and a descriptive-analytical method. For this purpose, the prevalence of urban sprawl in the area under investigation was first verified using Shannon’s entropy method. Subsequently, the share of horizontal urban growth, which has faced Deylam with urban sprawl, was specified using the Holdren model. Next, the rate of horizontal growth for the period of investigation was calculated for the first time through application of the Digital Shoreline Analysis System to a study of horizontal urban growth. Eventually, the optimum size of Deylam  for the investigation period was obtained through subtraction of the share of growth calculated by the Holdren model from the total growth of the city, provided then through maps generated using ArcGIS 10. According to the calculations made using Shannon’s entropy, Deylam was expanded extensively at the beginning of the investigation period (i.e., February 16, 2005), undergoing 80.14 percent its maximum possible urban sprawl. Moreover, 62.9 percent of the urban growth of the city in the investigation period resulted from the population growth, based on the Holdren model; therefore, 37.1 percent of the total growth is responsible for the urban sprawl of the city. The results demonstrated that Deylam has experienced growth rates of 19.08 and 23.11 m/year at its northern and southern edges with standard deviations of 4.5 and 4.1, respectively. At the northern edge, the growth rate of 7.08 m/year is due to the urban sprawl, and the 12-m/year rate has resulted from the population growth.  Along the same lines at the southern edge of the city, the growth rate of 8.57 m/year is due to the urban sprawl, and the 14.54-m/year rate has resulted from the population growth. The western and eastern edges of Deylam have not developed during the investigation period, because there have been natural barriers in these parts. Since the presented framework, implemented in this study, is easy to apply, and the procedure of calculation is clear, it may provide contributions in projects involving prevention of urban sprawl.